sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling buggrafted

alb_break_llc() decides whether to break LLC preference during active
load balance. It does so by testing that every runnable fair task on the
source rq prefers its LLC:

	env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable

But the two counters cover different sets. nr_pref_llc_running is updated
in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued,
so it follows queued tasks. h_nr_runnable is updated in set_delayed()/
clear_delayed() and drops delay-dequeued tasks.

So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted
in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks,
alb_break_llc() returns false, and active balance is free to pull a task
off its preferred LLC. Active balance only moves runnable tasks, and this
is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB
skips the per-task test in can_migrate_task(). The runnable set is the one
we want.

Fix it on the counter side. A task should be counted in
nr_pref_llc_running exactly while it is both queued on its preferred LLC
(pref_llc_queued) and runnable (!sched_delayed). Define that membership
once in task_pref_llc_runnable(), and adjust the counter only through
pref_llc_running_inc()/pref_llc_running_dec() from the four sites that
change either input: account_llc_enqueue(), account_llc_dequeue(),
set_delayed() and clear_delayed(). Gating every update on the same
predicate keeps the delay, wake and dequeue paths from double-counting
or underflowing; see the comments at those sites for the ordering.

nr_llc_running and sd->llc_counts are not touched and stay on queued
semantics.

Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC")
Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/
Reported-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Suggested-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Kayra Cizmeci <kayracizmeci@gmail.com>
Cc: <stable@kernel.org> # v7.2.x
Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com

1 files changed, 173 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/debugfs-hisi-sec b/Documentation/ABI/testing/debugfs-hisi-sec
new file mode 100644
index 000000000..676e2dc2d
--- /dev/null
+++ b/Documentation/ABI/testing/debugfs-hisi-sec
@@ -0,0 +1,173 @@
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/clear_enable
+Date:		Oct 2019
+Contact:	linux-crypto@vger.kernel.org
+Description:	Enabling/disabling of clear action after reading
+		the SEC debug registers.
+		0: disable, 1: enable.
+		Only available for PF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/current_qm
+Date:		Oct 2019
+Contact:	linux-crypto@vger.kernel.org
+Description:	One SEC controller has one PF and multiple VFs, each function
+		has a QM. This file can be used to select the QM which below
+		qm refers to.
+		Only available for PF.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/alg_qos
+Date:		Jun 2021
+Contact:	linux-crypto@vger.kernel.org
+Description:	The <bdf> is related the function for PF and VF.
+		SEC driver supports to configure each function's QoS, the driver
+		supports to write <bdf> value to alg_qos in the host. Such as
+		"echo <bdf> value > alg_qos". The qos value is 1~1000, means
+		1/1000~1000/1000 of total QoS. The driver reading alg_qos to
+		get related QoS in the host and VM, Such as "cat alg_qos".
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/dev_usage
+Date:		Mar 2026
+Contact:	linux-crypto@vger.kernel.org
+Description:	Query the real-time bandwidth usage of device.
+		Returns the bandwidth usage of each channel on the device.
+		The returned number is in percentage.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/qm_regs
+Date:		Oct 2019
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump of QM related debug registers.
+		Available for PF and VF in host. VF in guest currently only
+		has one debug register.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/current_q
+Date:		Oct 2019
+Contact:	linux-crypto@vger.kernel.org
+Description:	One QM of SEC may contain multiple queues. Select specific
+		queue to show its debug registers in above 'regs'.
+		Only available for PF.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/clear_enable
+Date:		Oct 2019
+Contact:	linux-crypto@vger.kernel.org
+Description:	Enabling/disabling of clear action after reading
+		the SEC's QM debug registers.
+		0: disable, 1: enable.
+		Only available for PF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/err_irq
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the number of invalid interrupts for
+		QM task completion.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/aeq_irq
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the number of QM async event queue interrupts.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/abnormal_irq
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the number of interrupts for QM abnormal event.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/create_qp_err
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the number of queue allocation errors.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/mb_err
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the number of failed QM mailbox commands.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/status
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the status of the QM.
+		Two states: work, stop.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/diff_regs
+Date:		Mar 2022
+Contact:	linux-crypto@vger.kernel.org
+Description:	QM debug registers(regs) read hardware register value. This
+		node is used to show the change of the qm register values. This
+		node can be help users to check the change of register values.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/qm_state
+Date:		Jan 2024
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the state of the device.
+		0: busy, 1: idle.
+		Only available for PF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/dev_timeout
+Date:		Feb 2024
+Contact:	linux-crypto@vger.kernel.org
+Description:	Set the wait time when stop queue fails. Available for both PF
+		and VF, and take no other effect on SEC.
+		0: not wait(default), others value: wait dev_timeout * 20 microsecond.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/qm/dev_state
+Date:		Feb 2024
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the stop queue status of the QM. The default value is 0,
+		if dev_timeout is set, when stop queue fails, the dev_state
+		will return non-zero value. Available for both PF and VF,
+		and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/sec_dfx/diff_regs
+Date:		Mar 2022
+Contact:	linux-crypto@vger.kernel.org
+Description:	SEC debug registers(regs) read hardware register value. This
+		node is used to show the change of the register values. This
+		node can be help users to check the change of register values.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/sec_dfx/send_cnt
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the total number of sent requests.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/sec_dfx/recv_cnt
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the total number of received requests.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/sec_dfx/send_busy_cnt
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the total number of requests sent with returning busy.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/sec_dfx/err_bd_cnt
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the total number of BD type error requests
+		to be received.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/sec_dfx/invalid_req_cnt
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the total number of invalid requests being received.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:		/sys/kernel/debug/hisi_sec2/<bdf>/sec_dfx/done_flag_cnt
+Date:		Apr 2020
+Contact:	linux-crypto@vger.kernel.org
+Description:	Dump the total number of completed but marked error requests
+		to be received.
+		Available for both PF and VF, and take no other effect on SEC.
+
+What:           /sys/kernel/debug/hisi_sec2/<bdf>/cap_regs
+Date:           Oct 2024
+Contact:        linux-crypto@vger.kernel.org
+Description:    Dump the values of the qm and sec capability bit registers and
+                support the query of device specifications to facilitate fault locating.
+                Available for both PF and VF, and take no other effect on SEC.